System for the ventilation of buildings

ABSTRACT

A system for the ventilation of buildings, comprising vertical and concentrical exhaust and injection ducts extending from a fan section located in the room to be vented through a damper section comprising adjustable dampers for controlling the ventilation, to a roof hood comprising an outer wall and a partition dividing said roof hood into two separate outlet spaces, one for each duct, said outer wall and partition being made of a plastic material and being proportioned so as to be packable together with said fan section and damper section, respectively, when shipping said ventilation system. The roof hood may be manufactured by pouring at least said partition from a plastic foam.

United States Patent [191 Peill et al. [451 Mar. 27, 1973 SYSTEM FOR THE VENTILATION OF [56] References Cited BUILDINGS UNITED STATES PATENTS [75] Inventors: .Jurgen Eberhardt Peill'; Alf Ger- 3,557,681 1/1971 Knstlansen ..98/33 R fits; MIMI" 05m", 3,599,865 8/1971 Krisu'ansen ..98/32 x Canning, N.S., Canada; Christian Karmark Andersen, Naestved, Primary Examiner william F. ODea Denmark Assistant Examiner-Peter D. Ferguson 73 Assignee: 'Nordisk Ventilator Co. Aktiesekkab, Ammer'mchard Sughme Naestved, Denmark [57] ABSTRACT [22] Filed: 1971 A system for the ventilation of buildings, comprising [21] Appl N04 197,059 vertical and concentrical exhaust and injection ducts extending from a fan section located in the room to be vented through a damper section comprising adjusta- [30] Foreign Application Priority Data ble dampers for controlling the ventilation, to a roof hood comprising an outer wall and a partition dividing Nov. 16,1970 Canada ..98,212 saidroof hood into two separate outlet Spaces, one for each duct, said outer wall and partition being made of U.S- Cl- R, a material and proportioned so as to be [51] Int. Cl. ..F24f 7/06 pagkable together with said fan ection and damper [58] Field of Search ..98/33 R, 33 A, 43

section, respectively, when shipping said ventilation system. The roof hood may be manufactured by pour- 10 Claims, 8 Drawing Figures PATENTFDHARZYISR 3 722,395

SHEET 3 OF 6 o m -T a P? 13 2 23 F/L'i' 1 SYSTEM FOR TIIE VENTILATION F BUILDINGS This invention relates to building ventilation systems and more particularly to a system for the ventilation of agricultural buildings such as stables, comprising fan means and control devices attached thereto for producing an air flow through the interior of such a building, which is constant in time and is adapted to the characteristics of said building, so that a fully automatic, draughtless ventilation thereof is obtained.

Ventilation systems of this kind comprises injection and exhaust ducts for connecting the interior of the building to the ambient air through a roof hood located above the roof of the building, which ducts are interconnected by a passage of variable cross-sectional area, by means of which a smaller or greater part of the air exhausted from the interior of the building may be recirculated into the injection duct. The supply of fresh air as well as the amount of recirculated air is usually controlled by adjustable damper means, by means of which the ventilation may be adjusted to any desired value between a maximum supply of fresh air, in which case the interior of the building is fully exposed to the ambient air through the injection and exhaust ducts, whereas the passage between said ducts is closed, so that no recirculation takes place, and a total recirculation, in which casethe passage between the ducts is fully open, whereas the part of each duct situated between said passage and the roof outlet of the duct is closed. The fan means is constantly operated, so that the volume of air supplied to the interior of the building and the volume of air exhausted therefrom per time unit equal each other and are maintained at constant values.

The ventilation provided by such a system is controlled in dependence on inter alia, outdoor weather conditions, so that in warm summer periods the damper means is adjusted to a maximum supply of fresh air, whereas in cold winter periods a total recirculation is provided without access for the ambient air.

In known systems of this kind the problem often arises that in periods of low outdoor temperature there is a material risk of water condensation on various parts of the system, which are normally made from simple metal plate. This applies particularly to such parts which are in relatively close contact with both the cold ambient air which is to be injected into the building, and the warmer air exhausted therefrom. A part of the system which is especially subject to such a risk is the roof hood which comprises outlet passages for both the injection and the exhaust duct, said passages being often separated by a simple partition. Such a water condensation is a most undesirable phenomenon in ventilation systems of the kinddescribed owing to the fact that the water condensed may be able to drip down into the stable, which may be very harmful to the health of the animals, particularly in poultry farming, because this condensed water may be polluted with detrimental gases, dirt etc. originating from the stable or with metal compounds formed by chemical reactions between the exhaust air and the various metal parts of the duct system. Furthermore, the water condensation may produce ice formations and expose metal parts of the duct system to severe corrosion.

It is an object of the present invention to provide an improved ventilation system in which the risk of water condensation is greatly reduced.

A further object of the invention is the provision of an improved roof hood for use in ventilation systems of a the kind described.

roof hood which, for shipping purposes, in order to reduce I freight volume and costs, can be packed together with other parts of the system in a simple and economical manner.

It is also an object of the invention to provide methods for manufacturing a roof hood for use in a ventilation system of the kind described.

The invention has also for its object to provide a method for packing together individual parts of a ventilation system in order to reduce freight volume.

In accordance herewith, the invention provides a system for the ventilation of buildings, for example stables or barns, comprising substantially vertical injection and exhaust ducts of circular cross-section, of which the injection duct is arranged concentrically around the exhaust duct, said ducts being terminated in one end by a combined fan and outlet section, which comprises a fan driving motor arranged in the exhaust duct and being operatively connected with a fan wheel, which is provided with two concentric, rigidly interconnected sets of vanes of the type used in axial flow fans, one set of which is located in the exhaust duct and the other in the injection duct, as well as injection and exhaust outlets connecting the interior of the building, for example the stable, to said injection ductand said exhaust duct respectively, whereas said ducts are 'terminated in the other end by a roof hood which is detachably connected to the ducts and is divided by means of a partition into two mutually separated outlet passages for connecting each of the two ducts to the ambient air, the outlet passage of said injection duct being shielded upwardly by the outer wall of the roof hood, while between said combined fan and outlet section and said roof hood a damper section is provided, in which the upper part of the partition between said exhaust and injection ducts is broken away forming thereby a passage between said ducts for recirculating part of the exhaust air flow to the injection duct, said damper section comprising furthermore adjustable damper means formed by two semi-cylindrical damper members, which are pivotable between two extreme positions, in one of which the exhaust and injection ducts are fully open, whereas said recirculation passage is fully closed, while in the other extreme position the exhaust and injection ducts are fully closed to the ambient air, whereas said recirculation passage is fully open, wherein the outer wall and the partition of said roof hood are manufactured from a plastic material as individual parts, which are adapted for being assembled when installing said ventilation system in said building, and wherein said partition is formed by a substantially cylindrical tubing, the inner diameter of which is slightly larger than the outer diameter of the partition between said concentrical exhaust and injection ducts, and the axial length of which is smaller than the axial length of the lower part of said damper section having an unbroken partition between said exhaust and injection ducts, while said outer wall if formed by a surface of revolution having parallel and circular upper and lower edges, the diameter of said lower edge being at least equal to the largest cross-sectional dimension of said combined fan and outlet section and exceeding he diameter of said upper edge, which is adapted for being connected with the top end of said cylindrical tubing.

By constructing the roof hood in accordance with the invention of a plastic material, considerably enhanced heat insulation properties of the walls of said roof hood is obtained, as a result of which the risk of water condensation is materially reduced.

Furthermore, by proportioning the two individual parts formed by the outer wall and the partition of said roof hood in the manner indicated, it becomes possible to pack one of said parts, viz. the outer wall, together with the fan and outlet section of the ventilation system and the other part, i.e., the partition, together with the damper section, so that by shipping the entire system one package and thus a considerable freight volume is saved and a corresponding reduction in freight costs is obtained.

The plastic material of which said parts of the roof hood is made, may for example be a fiberglass-reinforced plastic.

In a preferred embodiment of a ventilation system according to the invention a roof hood is used, in which at least said partition is formed by a double-walled construction with a cavity between the walls.

In a further development of such a roof hood said cavity may be filled with a porous insulating material.

According to the invention one method for manufacturing a roof hood of the kind described involves the steps of pouring at least the partition of said roof hood from a plastic foam and providing subsequently a coating of a harder plastic material thereon.

A roof hood of the kind mantioned may also, according to the invention, be manufactured by another, very simple and cheap method involving the steps of pouring at least said partition from a structural foam plastic material, during the hardening of which porosities are formed in the interior of said material, whereas surface zones thereof becomes relatively hard and solid.

A method for packing individual parts of a ventilation system of the kind described involves the steps of packing the outer wall and the partition of said roof hood together with said fan and outlet section and said damper section, respectively, so that two packages are obtained each having substantially the same volume as one of said sections.

An embodiment of the invention. will now be described in greater detail with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic cross-sectional view of the complete ventilation system,

FIG. 2 shows a cross-sectional view of one embodiment ofa roof hood used in the system as shown in FIG. 1

FIGS. 3 and 4 illustrate how the roof hood shown in FIG. 2 may be packed together with other sections of the system shown in FIG. 1 for the purpose of reducing freight volume,

FIG. 5 shows a cross-sectional view of another embodiment of a roof hood for use in the system as shown in FIG. 1,

FIGS. 6 and 7 illustrate how the roof hood shown in FIG. 5 may be packed together with other sections of the system shown in FIG. 1 for the purpose of reducing freight volume,

FIG. 8 shows a cross-sectional view of a particular embodimer t of a partition for use in a roof hood as shown in FIG. 5.

The ventilation system shown in FIG. 1 of the drawings comprises three main parts, viz. a roof hood 1, a control or damper section 2 and a fan and outlet section 3, of which the sections 2 and 3 are intercom necte'd by means of a duct section 4 shown in dotted lines, said section being formed by concentric tube sections and forming parts of an exhaust duct 5 and an injection duct 6 arranged concentrically around said exhaust duct, said exhaust and injection ducts extending throughout the ventilation system from the roof hood 1 to the fan and outlet section 3.

This ventilation system is adapted for use in a building, for example a stable, so that the roof hood 1 is located above the roof of said building, whereas the fan and outlet section 3 is located directly below the ceiling of a room to be vented. The length of the duct section 4 is, therefore, adapted to the actual proportions of the building, in which the ventilation system is to be used.

The roof hood 1, which will be described in greater detail in the following with reference to FIG. 2 of the drawings, is, by means of a partition 7 forming a circular cylinder, divided into two spaces 8 and 9 forming outlet passages for connecting the exhaust duct 5 and the injection duct 6, respectively, to the ambient air. By means of flanges, of which only one is indicated in FIG. 1 by 10, the roof hood 1 is pivotably mounted on arms 11 secured to the top end of the damper section 2, so that it can be tilted and, thereby, provide access for inspection and cleaning of said damper section. On the opposite side of said ducts, snap springs 12 and 13 are secured to the roof hood 1 and the damper section 2, respectively, for fastening the roof hood to said damper section.

The fan and outlet section 3 comprises a fan driving motor 14, which is operatively connected to a fan wheel 15 carrying two concentric sets of vanes 16 and 17, of which the vanes 16 are secured in one end to a hub 18 and in the other end to one side of a ring 19, to the other side of which the vanes 17 are secured. The vanes 16 and 17 of the two sets have mutually opposite inclinations, so that the air flow produced by one vane set will be oppositely directed relative to that produced by the other; thus, in the example shown the air flow produced by the vane set 16 will be directed upwards and the air flow produced by the vane set 17 will be directed downwards.

The fan driving motor 14, the fan wheel 15 and the vane sets 16 and 17 are mounted in tube sections 20 and 21 defining the part of the exhaust and injection ducts 5 and 6 extending through the section 3, said tube sections 20 and 21 being arranged coaxially around the fan l4l7 in such a way that one tube section 20 is in alignment with the ring 19, whereas the other tube section 21 surrounds the outer vane set 17, the tube sections 20 and 21 being rigidly interconnected by means of connecting members 22.

The injection duct is at the bottom provided with a number of outlets in the form of nozzles 23, the axes of which extend perpendicularly to the axis of the ducts 5 and 6, said nozzles being equally spaced along the circumference of the injection duct with an angle of e.g., 30 between two nozzles succeeding each other, so that the total number of inject nozzles is 12; Each of the nozzles 23 comprises a pair of guide blades 24, which are individually adjustable so that the direction of the air injected from said nozzle into the room to be vented which is, for example, a stable or a barn, may be chosen in accordance with the characteristics of the room, particularly the presence of any flowhindrance in the vicinity of the nozzle. 5

The exhaust duct 5 is at the bottom connected to the interior of the stable or the barn through a conical outlet 25 which is closed by a grid 26 which serves for preventing greater particles of dirt etc. from entering the exhaust duct. For cleaning purposes said grid may be detachably mounted over the opening 25.

The control or damper section 2 has an outer wall in the form of a tube section 27 having the same diameter as the tubesection 21, which tube section 27 is by means of connecting members 28 rigidly connected to a concentrical, internal tube section 29 having the same diameter as the tube section 20, said tube section 29 extending, however, only through the lower portion of the damper section 2, whereas in the top portion thereof there is an opening 30 forming between the exhaust duct 5 and the injection duct 6 a passage, the magnitude of which can be varied by the damper means, which is in the embodiment shown constructed in such a way that by operating said damper means the passages through the exhaust and injection ducts are simultaneously controlled, so that said passages are fully blocked when the opening 30 has its maximum magnitude, whereas they are fully open when the opening 30 is closed. I

As shown in FIG. 1 said damper means is constructed as a single unit comprising two semi-cylindrical damper members 31, the diameter of which corresponds to the diameter of the tube section 29, which form the partition between the parts of the exhaust and injection ducts 5 and 6 extending through the damper section 2. The damper members 31 are journalled rigidly on shafts 32 and 33, which are perpendicular to the axis of the ducts 5 and 6 as well as to the axes of the semicylindrical members 31 themselves so as to be pivotable by rotation of said shafts. The shafts 32 and 33 are situated at one end edge 34 of each damper member 31, which is bevelled in such a way that said bevelled edges form the same angle with the separating plane of the members 31, when these members are in a position, in which they are aligned with the tube section 29.

Each of the damper members 31 is in the opposite end cut off along an end edge 35, which follows a curve forming the sectional curve between the tube section 27 and said member, when the members 31 are in a position, in which the bevelled edges 34 abut upon ,each other.,Furthermore, each of the dampers 31 is, at

the side edges thereof, provided with outwardly extending flanges 36, which lie in a common plane through the axis of said member such as shown in FIG. 3, and which have such a shape that they abut upon the tube section 27, when the damper members 31 are in the above-mentioned position with the bevelled edges 34 abutting upon each other. Thus, in the said position, the projections of the edges 35 of the damper members 31 and of the outer edges of the flanges 36 on a normal plane in the ducts will describe a circle, the radius of which corresponds to the inner radius of the tube section 27, so that in said position the parts of the exhaust and injection ducts situated above the damper members 31 are completely blocked by these members,

whereas the opening 30 has its maximum magnitude, so

that the air flow produced by the fan is completely recirculated. On the other hand, in a position inlwhich the flanges 36 abutupon each other, the exhaust and injection ducts 5 and 6'are completely open, whereas the passage formed by the opening 30 is completely blocked.

The position of the damper members 31 may be adjusted manually. However, in most cases an automatic control is preferred by which the adjustment of the position of the damper members is performed in dependence on temperature and/or humidity conditions in the room to be vented.

For this purpose, the ventilation system shown in FIG. 1 comprises a thermo-hydraulic control device 37 arranged within the damper section 2 in the axial line of the ducts, in whicha piston is moved, which effects movement of the members 31 through a suitable transmission arranged in a casing 38 which is secured to the tube section 29 by means of connecting members'39, and to the bottom of which said control device 37 is secured, which transmission comprises, for example, a rack which is rigidly connected to the piston in the device 37 and meshes with gears secured on the shafts 32 and 33, on each of which one of the members 31 is also secured. In order to facilitate movement of the members 31, counterweights 40 and 41 may be secured to the shafts 32 and 33, respectively. However, the more detailed construction of the control mechanism does not form part of the present invention and needs no further description.

As mentioned hereinb'efore, known ventilation systems of the kind described have the disadvantage I that during periods of low outdoor temperature there is a great risk of water condensing on parts of the system I which, at the same time, are exposed to both the cold ambient air which is to be injected into the building, and the warmer air exhausted therefrom..This is, of course, due to the fact that the moisture content of said warmer air is usually relatively high. A part of the system, which is in particular exposed to such a risk is the roof hood 1 comprising the outlet passages 8 and 9, through which warm air form the interior of the building and cold ambient air, respectively, is made to pass.

According to the invention, the risk of water condensing on the walls of the roof hood'is eliminated or at least greatly reduced by constructing the outer walls and the partition of said roof hood of a plastic material.

Referring now to FIG. 2 of the drawings, the roof hood 1 used in the ventilation system shown in FIG. 1 comprises two parts, one of which is formed by the partition 7 separating the outlet passages 8 and 9, whereas the other part is formed by the outer wall of the roof hood, said part being designated in FIG. 2 by reference number 42.

According to the invention, the partition 7 has the form of a tubing of circular cross-section, the inner diameter of which is slightly greater than the outer diameter of the partition between the exhaust and injection ducts 5 and 6, for example the tube section 29. In the embodiment shown in FIG. 2 this tubular partition 7 is, at the top end, provided with a circular collar hood 1 is in position on the damper section 2. Due to this shape, the roof hood 1 can, as mentioned with reference to FIG. 1, be easily tilted by means of the pivotable connection between the flanges and the arms 11 on the damper section 2 so as to provide access for inspection and cleaning of the damper section.

The outer wall 42 of the roof hood 1 forms a surface of revolution having parallel and circular lower and upper edges 45 and 46, respectively, of which the lower circular edge 45 has a diameter which is at least equal to the largest cross-sectional dimension of the fan and outlet section 3, that is to say that said diameter should at least be equal to the distance between the outlet openings of diametrically opposite nozzles 23. The upper circular edge 46 is shaped so as to receive the circumferential edge of the circular collar 43 at the top end of the partition 7, said edge having a diameter which slightly exceeds the diameter of the outer wall of the injection duct, for example the tube section 27.

By proportioning the tubular partition 7 and the outer wall 42 of the roof hood 1 in this way it becomes possible to pack said parts together with other sections of the ventilation system shown in FIG. 1 when shipping such a system. As a result hereof, a considerable reduction of freight volume is obtained. Particularly in connection with railway charter, a material reduction in freight costs is obtained thereby.

FIGS. 3 and 4 of the drawings illustrate how this advantage may 'be obtained in case of a roof hood as shown in FIG. 2. More particularly, FIG. 3 shows how the partition 7 of the roof hood 1 may be packed together with the damper section 2 in FIG. 1 by inserting said partition 7 in the damper section from the lower end thereof. Due to the relatively great length of the damper section, which is necessary for accommodating the device 37 of the thermo-hydraulic servomechanism in said section, sufficient place will be available for this purpose in the part of the damper section lying below the connecting members 28. By inserting the partition 7 in the damper section the circular collar 43 will abut upon the lower edge of the tube section 27 forming the outer wall of the damper section 2. The whole package obtained thereby will have a volume which is only slightly greater than that of the damper section alone.

FIG. 4 shows how the outer wall 42 of the embodiment of the roof hood shown in FIG. 2 may be packed together with the combined fan and outlet section 3 by placing it at the top end of said section with the upper circular edge 46 resting on a mounting ring 47 which is secured to the tube section 21 and serves for mounting the fan and outlet section 3 to the ceiling of the room to be vented.

When installing the ventilation system shown in FIG. 1 in a building, for example a stable or a barn, the partition 7 and the outer wall 42 of the roof hood 1, which during transport of the system have been packed as shown in FIGS. 3 and 4, are assembled by connecting the circumferential edge of the circular collar 43 of the partition 7 and the upper edge 46 of the outer wall 42 to each other by means of, for example, a synthetic adhesive.

In the roof hood thus obtained, the risk of water condensing will be very limited owing to the fact that the partition between the outlet spaces 8 and 9 is formed by a vertical, cylindrical tubing made of a plastic material, which has a low heat conductivity. As a result hereof, a relatively great temperature difference may exist between the surfaces of said partition facing the outlet spaces 8 and 9, respectively, so that the cold air passing through the space 9 connected to the injection duct 6 will not be able to effect a cooling of the surface of the partition facing the outlet space 8 to a temperature, at which water is condensed from the exhausted air passing through said outlet space. However, further enhanced heat insulation properties may, according to the invention, be obtained by providing on the surface of said partition facing the space 9 a layer 48 of a porous insulating material as shown in FIG. 2.

In FIG. 5 of the drawings another embodiment of the roof hood is shown, in which the partition between the outlet spaces 8 and 9 and the outer wall of said roof hood are designated by 49 and 50, respectively. The only difference between this embodiment and the roof hood 1 shown in FIG. 2 consists in that the partition 49 which has downwardly directed extensions 51 is, in this case, formed by a cylindrical tubing without a circular collar at the top end, while the top end of the outer wall 50 is provided with a circular rim 52, the inner surface of which adjoins the top end of the partition 49. With the exception of this feature the embodiments shown in FIGS. 2 and Sam identical.

FIGS. 6 and 7 of the drawings illustrate how the individual parts 49 and 50 of the roof hood 1 shown in FIG. 5 may be packed together with the damper section 2 and the fan and outlet section 3, respectively, when shipping the ventilation system. It should be observed that the partition 49 may be completely contained in the damper section 2 so that, in this case, the whole package consisting of these two parts will have the same volume as the damper section alone and the partition 49 will be completely protected against damage during the transport. On the contrary, as shown in FIG. 7 the package consisting of the fan and outlet section 3 and the outer wall 50 of the roof. hood will have a slightly greater volume than in case of the embodiment shown in FIG. 2 owing to the fact that the top end'of the outer wall 50 will overlap the top end of the fan and outlet section 3.

As mentioned hereinbefore, enhanced heat insulation properties of the partition between the outlet spaces 8 and 9 of the roof hood 1 may be obtained by providing a layer 48 of a porous insulating material around said partition on the surface thereof facing the outlet space 9. However, according to the invention a still greater heat resistance may be obtained without the use of such an insulating layer by forming said partition as a double-walled cylindrical tubing comprising a cavity which contains just plain air or may be filled with a porous insulating material. FIG. 8 of the drawings shows a partition 53 of such a construction, which is adapted for use in a roof hood as shown in FIG. 5. The porous insulating material 54 in the cavity of said partition 53 may, for example, be a plastic foam.

A partition 53 of the construction shown in FIG. may, according to the invention, be manufactured by a method involving the steps of pouring said partition from a plastic foam andproviding subsequently a coating of a harder plastic material thereon. in this process, said plastic foam may, in order to obtain an improved rigidity of the construction, be poured around supporting ribs made of a fiberglass-reinforced plastic material. The coating of a harder plastic material may, for example, be applied by spraying.

However, the partition 53 may alternatively be manufactured by another very simple and cheap method involving the step of pouring said partition from a structural foam plastic material, during the hardening of which porosities are formed in the interior of said material, whereas surface zones thereof become relatively hard and solid. By means of this method, a double-walled partition is obtained comprising surface zones which are relatively hard and solid and between said zones an internal, porous insulating zone.

While it will be appreciated that the methods described above for manufacturing the partition of the roof hood as a double-walled construction are particularly suitable when forming said partition as shown in FIG. 5 without a circular collar at the top end thereof, it should be observed that the use of said methods is, of course, not restricted to this particular form of the roof hood. 7

What we claim is: 1

l. A system for the ventilation of buildings, for example stables, comprising substantially vertical injection and exhaust ducts of circular cross-section, of which the injection duct is arranged concentrically around the exhaust duct, said ducts being terminated in one end by a combined fan and outlet section, which comprises a fan driving motor arranged in the exhaust duct and being operatively connected with a fan wheel, which is provided with two concentric, rigidly interconnected sets of vanes of the type used in axial flow fans, one set of which is located in the exhaust duct and the other in the injection duct, as well as injection and exhaust outlets connecting the interior of the building, for example the stable, to said injection duct and said exhaust duct respectively, whereas said ducts are terminated inthe other end by a roof hood which is detachably connected to the ducts and is divided by means of a partition into two mutually separated outlet passages for connecting each of the two ducts to the ambient air, the outlet passage of said injection duct being shielded upwardly by the outer wall of the roof hood, while between said combined fan and outlet section and said roof hood a damper section is provided, in which the upper part of the partition between said exhaust and injection ducts is broken away forming thereby a passage between said ducts for recirculating part of the exhaust air flow to the injection duct, said damper section comprising furthermore adjustable damper means formed by two semi-cylindrical damper members, which are pivotable between two extreme positions, in one of which the exhaust and injection ducts are fully open, whereas said recirculation passage is fully closed, while in the other extreme position the exhaust and injection ducts are fully closed to the ambient air, whereas said recirculation passage is fully open, wherein the outer wall and the partition of said roof hood are manufactured from a lastic material as individual parts, which are adapted or being assembled wheninstalling said ventilation system in said building, and wherein said partition is formed by a substantially cylindrical tubing,

the inner diameter of which is slightly larger than the outer diameter of the partition between said concentrical exhaust and injection ducts, and the axial length of which is smaller than the axial length of the lower part of said damper section having an unbroken partition between said exhaust and injection ducts, while said tion of said roof hood is provided on the surface facing the outlet passage connected to said injection duct with a layer of a porous insulating material. 1

4. A system as claimed in claim 1, wherein at least.

the partition of said roof hood is formed by a doublewalled construction comprising a cavity between th walls.

5. A system as claimed in claim 4, wherein supporting ribs are provided in said cavity.

6. A system as claimed in claim 4, wherein said cavity is filled with a porous insulating material.

7. A system as claimed in claim 6, wherein said insulating material consists of a plastic foam.

8. A system as claimed in claim 1, wherein the partition of said roof hood is at the top end thereof provided with a circular collar, the outer diameter of which'is slightly greater than the diameter of the outer wall of said injection duct, the upper edge of the outer wall of said roof hood being proportioned so as to be connected to the circumferential edge of said collar.

9. A system as claimed in claim 7 wherein the walls of said roof hood partition are provided as non-porous surface layers of said plastic foam.

It A system as claimed in claim 7 wherein the walls of said "roof hood partition are provided as surface layers of a harder non-porous plastic material on said plastic foam and integral therewith. 

1. A system for the ventilation of buildings, for example stables, comprising substantially vertical injection and exhaust ducts of circular cross-section, of which the injection duct is arranged concentrically around the exhaust duct, said ducts being terminated in one end by a combined fan and outlet section, which comprises a fan driving motor arranged in the exhaust duct and being operatively connected with a fan wheel, which is provided with two concentric, rigidly interconnected sets of vanes of the type used in axial flow fans, one set of which is located in the exhaust duct and the other in the injection duct, as well as injection and exhaust outlets connecting the interior of the building, for example the stable, to said injection duct and said exhaust duct respectively, whereas said ducts are terminated in the other end by a roof hood which is detachably connected to the ducts and is divided by means of a partition into two mutually separated outlet passages for connecting each of the two ducts to the ambient air, the outlet passage of said injection duct being shielded upwardly by the outer wall of the roof hood, while between said combined fan and outlet section and said roof hood a damper section is provided, in which the upper part of the partition between said exhaust and injection ducts is broken away forming thereby a passage between said ducts for recirculating part of the exhaust air flow to the injection duct, said damper section comprising furthermore adjustable damper means formed by two semi-cylindrical damper members, which are pivotable between two extreme positions, in one of which the exhaust and injection ducts are fully open, whereas said recirculation passage is fully closed, while in the other extreme position the exhaust and injection ducts are fully closed to the ambient air, whereas said recirculation passage is fully open, wherein the outer wall and the partition of said roof hood are manufactured from a plastic material as individual parts, which are adapted for being assembled when installing said ventilation system in said building, and wherein said partition is formed by a substantially cylindrical tubing, the inner diamEter of which is slightly larger than the outer diameter of the partition between said concentrical exhaust and injection ducts, and the axial length of which is smaller than the axial length of the lower part of said damper section having an unbroken partition between said exhaust and injection ducts, while said outer wall is formed by a surface of revolution having parallel and circular upper and lower edges, the diameter of said lower edge being at least equal to the largest cross-sectional dimension of said combined fan and outlet section and exceeding the diameter of said upper edge, which is adapted for being connected with the top end of said cylindrical tubing.
 2. A system as claimed in claim 1, wherein said plastic material consists of a fiber-glass-reinforced plastic material.
 3. A system as claimed in claim 1, wherein the partition of said roof hood is provided on the surface facing the outlet passage connected to said injection duct with a layer of a porous insulating material.
 4. A system as claimed in claim 1, wherein at least the partition of said roof hood is formed by a double-walled construction comprising a cavity between the walls.
 5. A system as claimed in claim 4, wherein supporting ribs are provided in said cavity.
 6. A system as claimed in claim 4, wherein said cavity is filled with a porous insulating material.
 7. A system as claimed in claim 6, wherein said insulating material consists of a plastic foam.
 8. A system as claimed in claim 1, wherein the partition of said roof hood is at the top end thereof provided with a circular collar, the outer diameter of which is slightly greater than the diameter of the outer wall of said injection duct, the upper edge of the outer wall of said roof hood being proportioned so as to be connected to the circumferential edge of said collar.
 9. A system as claimed in claim 7 wherein the walls of said roof hood partition are provided as non-porous surface layers of said plastic foam.
 10. A system as claimed in claim 7 wherein the walls of said roof hood partition are provided as surface layers of a harder non-porous plastic material on said plastic foam and integral therewith. 